It is all about comfort

The term 'thermal comfort' describes a person's state of mind in terms of whether they feel too hot or too cold.

Can you measure thermal comfort? Or can you feel it?

Thermal comfort is very difficult to define because it is based on a range of environmental, work-related and personal factors when deciding what makes a comfortable workplace temperature.

The thermal comfort is basically describing a thermal environment that satisfies the majority of people in the workplace. Thermal comfort is not measured by room temperature, but by the number of employees complaining of thermal discomfort.

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What is thermal comfort?

Thermal comfort is affected by two types of parameters.

1.physical parameters

Such as air temperature (alternatively operative air temperature), vertical air temperature difference, mean radiant temperature, radiant temperature asymmetry (otherwise floor surface temperature), relative humidity and air speed (velocity including draughts and ventilation), and

2.physiological parameters

Such as metabolic rate and clothing insulation.

Effects of air movement on people - how draught influnces comfort

Air velocity Probable impact
Up to 0.25 m/s Unnoticed
0.25 to 0.5 m/s Pleasant
0.5 to 1 m/s Generally pleasant, but causes a constant awareness of air movement
1 to 1.5 m/s From slightly drafty to annoyingly drafty
Above 1.5 m/s Requires corrective measures if work and health are to be kept at comfortable levels

How to control thermal comfort?

[* extract good info from this source]

Can you adapt to the thermal environment?

People adapt their behaviour to cope with their thermal environment, eg adding or removing clothing, unconscious changes in posture, choice of heating, moving to or away from cooling/heat sources etc.

The problems arise when this choice (to adapt) is removed, and people are no longer able to adapt. In some instances the environment within which people work is a product of the processes of the job they are doing, so they are unable to adapt to their environment.

What is the next?

Adapted versus not-adapted?

There are quite big differences between the European recommendations and those listed by ASHRAE. One major reason is that ASHRAE requirements are minimum code requirements, where the basis for design is adapted people, while the European recommendations are for un-adapted people (visitors). Adapted people are considered those who entered a room and are already acclimatized to the situation in the room, i.e. approximately 15 minutes after entering a room. Visitors are people who just entered a room and are assessing the situation in the room at that moment of entering.

[* Picture shows the required ventilation rates from standard EN15251 compared to ASHRAE 62.1.]


Who should we ventilate for? For people just entering the room (un-adapted) or for people already occupying a room (adapted)? Here the philosophy adopted by ASHRAE 62.1 and EN15251 differs. But should it really be one or the other? In a conference room, auditorium or lecture room most people enter at the same time. It then takes some time before the odour level has reached an unacceptable level and meanwhile people adapt. In this case it may be appropriate to require a ventilation rate based on adapted persons. There may be other spaces where you would design for un-adapted people, e.g. in a first class restaurant, offices, and department stores. It seems logical that more differentiated criteria could be used.

[*source Bjarne Olesen]


Adaptative comfort criteria must be adopted whenever possible when applying nZEB!

Adaptation from ISO 7730:2005 (E) states the following: In determining the acceptable range of operative temperature according to this International Standard, a clothing insulation value that corresponds to the local clothing habits and climate shall be used.

In warm or cold environments, there can often be an influence due to adaptation. Apart form clothing, other forms of adaptation, such as body posture and decreased activity, which are difficult to quantify, can result in the acceptance of higher indoor temperatures. People used to working and living in warm climates can more easily accept and maintain a higher work performance in hot environments than those living in colder climates (see ISO 7933 and ISO 7243).

Extended acceptable environments may be applied for occupant-controlled, naturally conditioned, spaces in warm climate regions or during warm periods, where the thermal conditions of the space are regulated primarily by the occupants through the opening and closing of windows. Field experiments have shown that occupants of such buildings could accept higher temperatures than those predicted by the PMV. In such cases, the thermal conditions may be designed for higher PMV values than those given in Clause 6 and Annex A.

[* source]